1. Field of the Invention
This invention relates to the regulation of the fuel to oxygen ratio in internal combustion engines. One particularly important practical application of this invention is in the adjustment of the fuel-to-oxygen ratio at startup ignition of the combustion engine. The invention is not intended to be limited to any particular engine and specifically includes engines which burn gaseous fuel and air. An example of one such engine to which the invention relates is a typical gas turbine engine.
2. Description of the Prior Art
While this invention relates in general to engines which burn a mixture of oxygen and fuel in the proper ratio, the particular problems to which this invention is directed are acutely present in a low BTU gas turbine at startup ignition. Some particular problems solved by the invention will therefore be discussed as they relate to a low BTU gas burning turbine engine and, in particular to the startup ignition period of operation.
With particular reference to combustion engines which generate power from the combustion of a gaseous fuel with the oxygen in air, the ratio of fuel mass to oxygen mass which is required for combustion has been approximated by providing a volume of fuel at a fixed pressure through a fixed size inlet nozzle for combustion with a volume of air. The pressure and the nozzle size were fixed so that the amount of fuel injected approximated the amount necessary for proper combustion with the oxygen in the intake air volume. A problem associated with this arrangement is that the mass of oxygen in the air taken into the combustion chamber does not remain constant as various conditions change such as ambient air temperature or pressure. It is understood that by "ambient air temperature or pressure" it is intended to mean the conditions of the inlet air whether from the atmosphere or from a closed supply system. Thus, the amount of fuel which enters into the combustion chamber is not always in the proper ratio with the air to permit efficient combustion. The problem is particularly acute in gas turbine engines which burn low BTU fuel. The inefficient burning caused by the improper fuel/air ratio is particularly noticeable at startup ignition of such engines because startup ignition will not occur unless the ratio of the fuel to air mass is proper. Thus, in such cases not only is the burning efficiency decreased by the improper ratio of fuel to air mass during normal operation but all use of the engine may be prevented because it will not start.
Previous attempts directed toward achieving the proper ratio of the fuel to air mass during the startup ignition period of operation included adjusting the voltage to the ignition spark plugs to attempt to generate enough heat to obtain a startup ignition even when the mixture was not proper. Such attempts have not been successful.
It was further found that a valve in the fuel supply line having a single fixed pressure setting would not provide the proper fuel/air mixture for startup ignition under all variable conditions affecting the oxygen mass content of the ambient air.
The present invention solves the problem of ignition in turbine engines by automatically adjusting the fuel flow valve to cause the proper fuel/air diferential pressure corresponding to the desired fuel/air mass ratio to occur during ignition at any particular ambient air temperature.